All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background.
Disclosed in the embodiments herein is a charge generating device, such as a corona, having a charge generating shield onto which titanium has been vacuum deposited.
Generally, the process of electrostatographic reproduction is initiated by substantially uniformly charging a photoreceptive member, followed by exposing a light image of an original document thereon. Exposing the charged photoreceptive member to a light image discharges a photoconductive surface layer in areas corresponding to non-image areas in the original document, while maintaining the charge on image areas for creating an electrostatic latent image of the original document on the photoreceptive member. This latent image is subsequently developed into a visible image by a process in which a charged developing material is deposited onto the photoconductive surface layer, such that the developing material is attracted to the charged image areas on the photoreceptive member. Thereafter, the developing material is transferred from the photoreceptive member to a copy sheet or some other image support substrate to which the image may be permanently affixed for producing a reproduction of the original document. In a final step in the process, the photoconductive surface layer of the photoreceptive member is cleaned to remove any residual developing material therefrom, in preparation for successive imaging cycles.
Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The above described electrostatographic reproduction process is well known and is useful for both digital copying and printing as well as for light lens copying from an original. In many of these applications, the process described above operates to form a latent image on an imaging member by discharge of the charge in locations in which light from a lens, laser, or LED discharges a charge. Such printing processes typically develop toner on the discharged area, known as DAD, or “write black” systems. Light lens generated image systems typically develop toner on the charged areas, known as CAD, or “write white” systems. The embodiments of the present disclosure apply to both DAD and CAD systems.
Generally, corona generating devices are utilized to apply a charge to the photoreceptive member. In a typical device, a suspended electrode, or so-called coronode, comprising a thin conductive wire, is partially surrounded by a conductive shield with the device being situated in close proximity to the photoconductive surface. The coronode is electrically biased to a high voltage potential, causing ionization of surrounding air which results in the deposit of an electrical charge on an adjacent surface, namely the photoconductive surface of the photoreceptive member.
Corona generating devices are well known, corona devices aid the transfer of the developed toner image from a photoconductive member to a transfer member. Likewise, corona devices aid the conditioning of the photoconductive member prior to, during, and after deposition of developer material thereon to improve the quality of the electrophotographic copy produced thereby. Both direct current (DC) and alternating current (AC) type corona devices are used to perform these functions.
One form of a corona charging device comprises a corona electrode in the form of an elongated wire connected by way of an insulated cable to a high voltage AC/DC power supply. Such corona generating devices may use a variety of biasing techniques. The corona wire is partially surrounded by a conductive shield. The photoconductive member is spaced from the corona wire on the side opposite the shield. The coronode, for example, may be provided with a DC voltage, while the conductive shield is electrically grounded and the photoconductive surface to be charged is mounted on a grounded substrate, spaced from the coronode opposite the shield. Alternatively, the corona device may be biased in a manner wherein the flow of ions from the electrode to the photoconductive surface is regulated by an AC corona generating potential applied to the conductive wire electrode and a DC potential applied to the conductive shield partially surrounding the electrode. The DC potential allows the charge rate to be adjusted, making this biasing system useful for self-regulating systems. Various other corona generating biasing arrangements are known in the art and will not be discussed in great detail herein.
Other forms of corona charging devices are pin corotrons and scorotrons. The pin corotron comprises an array of pins integrally formed from a sheet metal member that is connected by a high voltage cable to a high voltage power supply. The sheet metal member is supported between insulated end blocks and mounted within a conductive shield. The photoconductive member to be charged is spaced from the sheet metal member on the opposite side of the shield. The scorotron is similar to the pin corotron, but is additionally provided with a screen or control grid disposed between a coronode and the photoconductive member. The conductive shield may form a generally U-shaped cross-sectional configuration substantially surrounding the electrode wire. The screen is held at a lower potential approximating the charge level to be placed on the photoconductive member. The scorotron provides for more uniform charging and prevents over charging.
Still other forms of corona charging devices include a dicorotron. The dicorotron comprises a coronode having a conductive wire that is coated with an electrically insulating material. When AC power is applied to the coronode by way of an insulated cable, substantially no net DC current flows in the wire due to the thickness of the insulating material. Thus, when the conductive shield forming a part of dicorotron and the photoconductive member passing thereunder under at the same potential, no current flows to the photoconductive member or the conductive shield. However, when the shield and photoconductive member are at different potentials, for example, when there is a copy sheet attached to the photoconductive member to which toner images have been electrostatically transferred thereto, an electrostatic field is established between the shield and the photoconductive member which causes current to flow from the shield to ground.
When using corona generating devices, a problem arises in that various nitrogen oxide species are produced by the corona. While these nitrogen oxide species are adsorbed by solid surfaces, they have also been observed to be adsorbed by the conductive shield, the housing and various components located within proximity of the corona generating device.
The adsorption process can be a physically reversible process wherein the nitrogen oxide species once adsorbed by the surrounding components are desorbed gradually when the corona device is powered off for extended periods. However, the composition of the species absorbed may not necessarily be the same as the composition of the nitrogen species desorbed and it is well known that a conversion of NO2 to HNO3 may occur. What occurs in the practical sense is readily observable upon powering on the corona device, wherein a defect in copy quality occurs. Known as a parking deletion, this defect entails a line or band image deletion. Another defect may be noticed when the corona device is powered off and remains idle, in particular, a lower density image may appear across the width of the photoreceptor at a location opposite the corona generating device.
The noticeable effect of the above results in a narrow line or solid area images becoming blurred and appearing washed out, as opposed to being developed as a toner image. Over extended periods of idleness, where the photoreceptor is exposed to the desorbing nitrogen oxide species, the line defect and solid area deletions have been noticed to increase in severity. For the initial stage of exposure of the photoreceptor to the desorbing nitrogen oxide species, reaction between the photoreceptor and the nitrogen oxide species occurs primarily at the surface. But, after prolonged exposure, the reaction may penetrate the surface layer of the photoconductive member. Whereas in the former situation, it may be possible to rejuvenate the photoreceptor with a topical cleaning application, it is more difficult in the latter situation.
The prior art reveals various solutions to effect adsorption of the nitrogen oxide species and to retard the desorption effect. In FIG. 2 of U.S. Pat. No. 4,290,266, a dicorotron is disclosed wherein the conductive shield 34 in conjunction with the two vertically extending side panels 32 coated with an aluminum hydroxide electrically conductive film 40 containing particulate graphite and powdered nickel effectively forms a conductive cavity in FIG. 1 of the U.S. Pat. No. 4,290,266. This conductive cavity 41 is represented in FIG. 1 of the present invention. This film 40 resides also on conductive shield 34 and adsorbs and desorbs the nitrogen oxide species, to overall neutralize the nitrogen oxide species when they are generated.